This invention concerns in die tapping devices which are used to tap holes in workpieces being formed by dies installed in presses.
Such tapping devices have often been operated by the motion of the press, as described in U.S. Pat. No. 6,547,496. Since the tap drive is dependent on the sinusoidal press motion, significant limitations on tapping speed results, increasing the cycle time for the process.
Thus, electrical servo motor drives have been developed for in-die tapping units in which servo motors mounted to the tapping unit are used to drive the tap, as described in copending U.S. application Ser. No. 10/417,428, filed on Apr. 15, 2003.
The tap drive is made independent of the press motion by the use of servo motors, and this allows driving of the tap at maximum speed to reduce cycle times.
A significant problem is created by mounting a servo motor to a tapping unit in that the servo motor is thereby subjected to shock loading when the stripper plate impacts the workpiece and fixture, and suddenly decelerates the servo motor, shortening the service life of the motor.
Typically, spring mounted stripper plates carry the tapping units and the stripper plate springs have been relied on to reduce the shock loading of servo motors.
However, the stripper plates comprise a separately supplied component from the tapping unit, and the stripper plate springs are not designed specifically to adequately attenuate shock loading of the associated servo motor in this application.
The user of this equipment must therefore attempt to design proper stripper springs to reduce shock loading of the motors to acceptable. This necessity is often neglected to the detriment of the service life of the servo motors.
According, it is an object of the present invention to provide an effective shock protection for servo motor driven die tapping units which does not rely on stripper plate springs to reduce shock or require a special design of the stripper plate springs to provide shock protection.